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The mortality experience of a cohort of 1165 white male rubber workers with at least 1 part per million (ppm) per day of cumulative exposure to benzene (71432) was reexamined. At the manufacturing facilities where they were employed, natural rubber was dissolved in benzene and spread on a conveyor. The benzene was evaporated and recovered and the resultant thin film was stripped from the conveyor, rolled, and milled according to specifications. For the most part, employee 8 hour time weighted average exposures to airborne benzene were within the limits of the standard in effect at any given time during the history of operation of these facilities from 1939 to 1976. Neither the mortality from all causes of death combined nor the mortality from all malignant neoplasms combined was above the expected rate. However, there was a statistically significant increase in deaths from all lymphatic and hematopoietic neoplasms (standardized mortality ratio, 227), due primarily to increased death from leukemia and from multiple myeloma. A marked progressive increase in leukemia mortality was noted with increasing cumulative exposure to benzene. There was no apparent pattern in these deaths with regard to latency, which ranged from under 5 to over 30 years. Standardized mortality ratios for multiple myeloma did not increase with increasing exposure. Case control analysis confirmed the relationship of benzene exposure and leukemia. The authors conclude that an exponential decrease in the risk of death from leukemia could be achieved by lowering occupational exposure to benzene. A worker occupationally exposed to benzene at the average exposure level of 10ppm for 40 years would have an increased risk of death from leukemia of 154.5. If the average exposure were lowered to 1ppm, that excess risk would decrease to 1.7, and at 0.1ppm, the risk would reach background levels.